"We have been monitoring the recent reports suggesting that toxic chemicals may have been used as weapons in the Idlib province in Syria," Organisation for the Prohibition of Chemical Weapons chief Ahmet Uzumcu said.
"The matter is of serious concern," Uzumcu said in a statement, issued at the OPCW's Hague-based headquarters.
A monitoring group and opposition activists said six people, including three young children, were killed in the alleged regime gas attack in the village of Sarmin, in Idlib province 10 days ago.
The attack prompted outrage from rights group Amnesty International, which said it was further evidence of regime "war crimes".
Activists have accused the Syrian regime of using chlorine -- a toxic agent that can be considered a chemical weapon -- on civilian areas in the past.
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A report by the OPCW in January concluded "with a high degree of confidence" that chlorine gas had been used in attacks on three villages in Syria last year.
At least 13 people died in the attacks that were carried out from April to August, according to the report.
Uzumcu said Wednesday the OPCW would continue a current fact-finding mission into the use of "toxic chemicals for hostile purposes" in Syria.
After an August 2013 sarin attack outside Damascus that much of the international community blamed on President Bashar al-Assad's government, the regime agreed to turn over its chemical arsenal.
But Syria did not have to declare its stockpile of chlorine -- a toxic agent that can be considered a chemical weapon -- as part of a disarmament deal agreed in 2013 because it is widely used for commercial and domestic purposes.
The Assad regime and the rebels have accused each other of using chemical agents, including chlorine, in the nearly four-year war that has killed more than 210,000 people.